Detecting and reporting faults in solar thermal systems

ABSTRACT

A control system and a method are disclosed for detecting and reporting a variety of faults in solar thermal systems. Detected and reported faults include a low fluid condition in a closed loop of a solar thermal system in a drain-back configuration, a pressure drop in a closed of a solar thermal system in a glycol configuration, a pressure drop in a potable water portion of a solar thermal system of either configuration. Additionally, systems and methods are disclosed for detecting and reporting power outages and heat exchanger scaling, both of which may be experienced by a solar thermal system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/950,759, filed Jul. 19, 2007, which is incorporated by reference in its entirety.

BACKGROUND

1. Field of Art

This disclosure generally relates to the field of solar thermal systems. More particularly, it relates to systems and methods for detecting and reporting faults in solar thermal systems.

2. Description of the Related Art

A solar thermal system is a system which converts solar energy into thermal energy. Solar thermal systems provide heated water for residential or commercial buildings by combining solar thermal collectors with modern plumbing systems. A solar thermal collector is a unit specifically designed to absorb solar energy and transfer thermal energy to a fluid reservoir, thereby heating the fluid. Many varieties of solar thermal collectors exist. A solar thermal collector may employ a flat surface or a parabolic surface for absorbing solar energy. Additionally, a solar thermal collector may utilize evacuated tubes to reduce conductive heat loss, thereby improving the efficiency of the system. Other variations are possible.

Conventionally, fluid circulates through one or more solar thermal collectors within a closed loop and becomes heated over time. A solar thermal system is classified as active if it uses one or more pumps to circulate the fluid within the closed loop. As it circulates within the closed loop, the fluid passes through a heat exchanger. The heat exchanger transfers thermal energy from the fluid in the closed loop to water circulating in a building's potable water system. A storage mechanism within the potable water system stores this heated water and dispenses it as needed.

Though conventional solar thermal systems have significant environmental and economic benefits, they do have some shortcomings. For example, should the fluid in the closed loop freeze, solar thermal collectors may be severely damaged. To prevent freeze damage, either of two methods is conventionally used. A first method is to include a drain-back tank in the closed loop of an active solar thermal system. Such a solar thermal system is referred to as a drain-back system. When the closed-loop pump is off, the fluid in the closed loop drains from the solar thermal collectors and into the drain-bank tank. In a drain-back system, the fluid is typically water. A second method is to use a water/glycol or glycol thermal conducting fluid as the closed-loop fluid. For the sake of clarity, any such a solar thermal system is referred to herein as a glycol system. The glycol acts as an antifreeze agent to prevent freeze damage to solar thermal collectors.

Both drain-back and glycol systems require control methods to ensure their proper operation.

SUMMARY

Systems and methods are disclosed for detecting and reporting faults in solar thermal systems. In one embodiment, a solar thermal system is in a drain-back configuration and a fluid level switch is used to detect a low fluid condition within a closed loop of the system. Responsive to the low fluid condition, a controller shuts off a pump and transmits an alert. In another embodiment, a solar thermal system is in a drain-back configuration and a pressure transducer is used to detect a pressure drop within an open loop of the system. Responsive to the pressure drop, a controller shuts off a pump and transmits an alert.

In yet another embodiment, a solar thermal system is in a glycol configuration and a pressure transducer is used to detect a pressure drop within a potable water portion of the system. Responsive to the pressure drop, a controller turns off a pump in the potable water portion, transmits an alert, determines a risk of a glycol fluid overheating, calculates a delay based on the risk, and turns off a closed loop pump after the delay. In still another embodiment, a solar thermal system is in a glycol configuration and a controller is configured detect a loss of power for the system. Responsive to detecting the power loss, the controller determines a duration that the system was without power, determines a risk of a glycol fluid overheating during the duration, and, if the risk is above a threshold, transmits an alert.

In still another embodiment, a solar thermal system is in a glycol configuration and a controller detects a pressure drop within a closed-loop portion of the system. Responsive to the pressure drop, the controller turns off all pumps in the system and transmits an alert.

In still yet another embodiment, a controller is configured to report scaling within a heat exchanger included in a solar thermal system. The controller calculates a present solar thermal output and a previous solar thermal output, compares the present solar thermal output to the previous solar thermal output, and, if the difference between the present solar thermal output and the previous solar thermal output exceeds a threshold, transmits an alert.

The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the disclosed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed embodiments have other advantages and features which will be more readily apparent from the detailed description, the appended claims, and the accompanying figures (or drawings). A brief introduction of the figures is below.

Figure (FIG.) 1 a illustrates one embodiment of a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 1 b illustrates one embodiment of a closed-loop portion of a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 1 c illustrates one embodiment of a potable water portion of a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 1 d is a block diagram of one embodiment of a system for controlling a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 2 is a block diagram of one embodiment of a controller in accordance with the present invention.

FIG. 3 is a flowchart of a first process for controlling a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 4 is a flowchart of a second process for controlling a solar thermal system in a drain-back configuration in accordance with the present invention.

FIG. 5 a illustrates one embodiment of a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 5 b illustrates one embodiment of a first portion of a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 5 c illustrates one embodiment of a second portion of a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 5 d is a block diagram of one embodiment of a system for controlling a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 6 is a flowchart of a first process for controlling a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 7 is a flowchart of a second process for responding to a power outage within a solar thermal system in a glycol configuration in accordance with the present invention.

FIG. 8 is a flowchart of a process for reporting scaling in heat exchanger in accordance with the present invention.

DETAILED DESCRIPTION

The Figures (FIGS.) and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the disclosed systems and methods for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.

Drain-Back Systems

FIG. 1 a illustrates one embodiment of a drain-back system. The drain-back system comprises two portions: a closed-loop portion 190 and a potable water portion 191. A primary function of the closed-loop portion 190 is to heat a fluid using solar energy. A heat exchanger 135 transfers thermal energy from fluid circulating in the closed-loop portion 190 to potable water circulating in the potable water portion 191, thereby heating the potable water. A primary function of the potable water portion 191 is to deliver heated potable water to a hot water output 102. Thus, the heat exchanger 135 couples the two portions 190, 191. For illustrative clarity, however, the heat exchanger is presented herein as included solely within the closed-loop portion 191.

The closed-loop portion 190 includes a solar thermal collector 105. The solar thermal collector 105 absorbs solar energy and imparts thermal energy to fluid passing through it. In some embodiments, the closed-loop portion 190 includes multiple solar thermal collectors 105, thereby increasing the capacity of the system to collect solar energy and heat fluid. In such embodiments, the solar collectors 105 are typically interconnected such that they collectively operate upon a single fluid reservoir. The closed-loop portion also includes a closed-loop pump 110 with an input port and an output port, a drain-back tank 115, a fluid level switch 120, valves 125 a, 125 b, a relief valve 130 a, and the heat exchanger 135.

The potable water portion 190 includes a storage tank 145, a water heater 150, a potable pump 160 a with an input port and an output port, a flowmeter 165, valves 125 c . . . 125 f, relief valves 130 b, 130 c, a mixing valve 155, a first temperature sensor 140 a, a second temperature sensor 140 b, and a pressure transducer 180 a. The valves 125 a . . . 125 f and the relief valves 130 a . . . 130 c each have an input and an output. The mixing valve 155 has two inputs and one output.

Referring now to FIG. 1 b, the closed-loop portion 190 of the drain-back system of FIG. 1 a is detailed. As mentioned above, a primary function of the closed-loop portion 190 is to heat a fluid using solar energy. This is done by circulating the fluid through at least one solar thermal collector 105.

A closed-loop fill source 103 supplies fluid for the closed-loop portion 190. The closed-loop fill source 103 connects to the input port of the second valve 125 b. As such, the second valve 125 b regulates the inflow of fluid into the closed-loop portion 190. The output port of the second valve 125 b connects to a fluid line passing between a first port of the drain-back tank 115 and a first port of the heat exchanger 135. A second port of the heat exchanger 135 connects to the input port of the closed loop-pump 110. The output port of the closed-loop pump 110 connects to a first port of the solar thermal collector 105. A second port of the solar thermal collector 105 connects to a second port of the drain-back tank 115. A third port of the drain-back tank 115 connects to both the input of the first valve 125 a and the input of the first relief valve 130 a. The output of the first relief valve 130 a connects to a first vent 104 a. The output of the first valve 125 a connects to a second vent 104 b.

Thus, a closed loop exists via which fluid may flow through the solar thermal collector 105, the drain-back tank 115, the heat exchanger 135, and the closed-loop pump 110. The closed-loop pump 110 pumps the fluid around this closed loop. As previously described, the solar thermal collector 105 heats the fluid as it flows through the closed loop. The drain-back tank 115 collects the fluid when the closed-loop pump 110 is off, preventing freeze damage to the solar thermal collector 105. The fluid level switch 120 monitors the fluid level within the closed loop. As the fluid circulates, the heat exchanger 135 transfers thermal energy from the fluid in the closed-loop to water in a potable water portion 191 of the solar thermal system which also flows through the heat exchanger 135 via a third and a fourth port.

In one embodiment, the fluid level switch 120 is located within the drain-back tank 115. In one embodiment, the fluid level switch 120 is normally closed, signaling that there is sufficient fluid in the closed loop. If the fluid in the closed loop drops below a threshold, the fluid level switch 120 changes state (opens). In one embodiment, this threshold is determined by the physical placement of the fluid level switch 120 within the drain-back tank 115. In such an embodiment, the fluid level switch 120 changes state when the fluid level within the drain-back tank 115 drops below the placement of the fluid level switch 120.

Referring now to FIG. 1 c, the potable water portion 191 of the drain-back system of FIG. 1 a is detailed. As mentioned above, a primary function of the potable water portion 191 is to deliver heated potable water to a hot water output 102. This is done by circulating potable water through the heat exchanger 135 (shown as part of closed-loop portion 190 in FIG. 1 a and FIG. 1 b) and storing the subsequently heated water for later delivery.

A water supply 101 (e.g., a cold water supply) provides water for the potable water portion 191. In one embodiment, the water supply 101 connects to the input port of the fifth valve 125 e. As such, the fifth valve 125 e regulates the inflow of water into the potable water portion 191. The output port of the fifth valve 125 e connects to both the first input of the mixing valve 155 and a first port of the flowmeter 165. A second port of the flowmeter 165 connects to a first port of the storage tank 145. The first temperature sensor 140 a senses the temperature of the water passing between the flowmeter 165 and the storage tank 145.

A second port of the storage tank 145 connects to the input port of the potable pump 160 a. The pressure transducer 180 a senses the pressure of the water passing between the storage tank 145 and the potable pump 160.

The output port of the potable pump 160 a connects to the third port of the heat exchanger 135. The fourth port of the heat exchanger 135 connects to both the input of the third valve 125 c and the input of the fourth valve 125 d. The output of the third valve 125 c connects to a third vent 104 c. The output of the fourth valve connects to a third port of the storage tank 145. Thus, the fourth valve 125 d regulates the flow of water between the heat exchanger 135 and the storage tank 145. A fourth port of the storage tank 145 connects to a first port of the water heater 150. The second temperature sensor 140 b senses the temperature of the water passing between the storage tank 145 and the water heater 150. A second port of the water heater 150 connects to the second input of the mixing valve 155. Thus, the mixing valve 155 combines water from the water supply 101 with water from the water heater 150 to produce water of a desired temperature. The output of the mixing valve 155 connects to the input of the sixth valve 125 f. The output of the sixth valve 125 f regulates a hot water output 102 for the building being served by the drain-back system.

To relieve pressure within the potable water portion 191, additional ports on the storage tank 145 and the water heater 150 connect to the inputs of the second relief valve 130 b and the third relief valve 130 c respectively. The outputs of the second relief valve 130 b and the third relief valve 130 c connect to a fourth vent 104 d.

Within, the potable water portion 191, water initially flows from the water supply 101 to the storage tank 145. The water is then pumped by the potable pump 160 a through the heat exchanger 135 where it gains heat transferred from the fluid in the closed-loop portion 190. The water then flows from the heat exchanger 135 into the storage tank 145. Thus, the heat exchanger 135 stores heated water for later use. Heated water also flows from the storage tank 145 into the water heater 150 where it is stored for later use. In one embodiment, the water heater 150 provides supplemental heat to augment the water-heating capabilities of the drain-back system as necessary. Also, in some embodiments, water in the potable water portion 191 may be re-circulated through the heat exchanger 135 for additional heating.

Referring now to FIG. 1 d, a block diagram of one embodiment of a system for controlling the drain-back system of FIG. 1 a is presented. The system comprises a controller 170 which is communicatively coupled to a network 185. In one embodiment of the present invention, the network 185 is a partially public or a wholly public network such as the Internet. The network 190 can also be a private network or include one or more distinct or logical private networks (e.g., virtual private networks or wide area networks). Additionally, the communicative coupling between the controller 170 and the network 185 can be wire line or wireless (i.e., terrestrial-based or satellite-based transceivers).

The controller 170 is also communicatively coupled to the closed-loop pump 110, the potable pump 160 a, the fluid level switch 120, the pressure transducer 180, the first temperature sensor 140 a, the second temperature sensor 140 b, and the flowmeter 165. The network 185 is also communicatively coupled to a weather server 175. Thus, the controller 170 is able to communicate with the weather server 175 via the network 185. In one embodiment, the controller 170 monitors the temperature and pressure of water within the potable water portion 191 using information from the temperature sensors 140 a, 140 b and the pressure transducer 180 a. In one embodiment, the controller 170 also monitors the quantity of water within the potable water portion 191 using information from the flowmeter 165. The controller 170 monitors the level of fluid within the closed-loop portion 190 using information from the fluid level switch 120. In one embodiment, the controller 170 controls the operation of the closed-loop pump 110 and the potable pump 160 a.

FIG. 2 is a block diagram illustrating the hardware architecture of the controller 170 according to one embodiment. The controller 170 is a microprocessor based controller capable of communicating via a network 185. The controller 170 includes a processor 205, an operating memory module 210, a storage module 215, a program memory module 220, and an input/output module (“I/O module”) 225, all exchanging data with one another through a data bus 230. The controller 170 also includes a number of externally accessible input and output pins (not shown) allowing electrical signals to pass between the controller 170 and one or more external devices.

In one embodiment, the processor 205 is a conventional microprocessor and includes conventional arithmetic and logic elements for executing computer program instructions. In some embodiments, the processor 205 includes additional functional elements such as analog-to-digital converters, timers, clock generators, or digital-to-analog converters. The operating memory module 210 is a conventional computing memory such as a random-access memory (RAM) containing one or more registers for storing bytes of data. The storage module 215 is a conventional long term storage device, for example, conventional EEPROM or flash memory. The program memory module 220 comprises read-only memory for storage of executable computer program instructions. The I/O module 225 comprises memory registers and blocks of digital logic configured to support direct and networked communication between the controller 170 and one or more external devices in accordance with conventional communication protocols (e.g., the inter-integrated circuit protocol, commonly referred to as I²C).

Insufficient fluid within the closed-loop can lead to excessive wear on the closed-loop pump 110 causing it to break down prematurely. Insufficient fluid in the closed-loop may result from a number of factors including an inadequate initial fluid level or leaks. In one embodiment, the controller 170 prevents premature breakdown of the closed-loop pump 110 by monitoring the fluid level within the closed-loop portion 190 using the process depicted in the flowchart of FIG. 3. In one embodiment, the fluid level switch 120 is normally closed, signaling that there is sufficient fluid in the closed loop. If the fluid in the closed loop drops below a threshold, the fluid level switch 120 changes state (opens), and the controller 170 detects 305 the low fluid level. To protect the closed-loop pump 110, the controller 170 then shuts down 310 all operating pumps. In one embodiment, the controller 170 shuts down only the closed-loop pump 110. After shutting down 310 all pumps, the controller transmits 315 one or more alerts over the network 185 to report the low fluid condition. An alert may be transmitted 315 via email, a short message service (SMS), or any other suitable method for transmitting 315 an alert over the network 185.

In one embodiment, the alerts notify service personnel or the owners of the system of the low fluid condition, allowing appropriate service actions to be performed on the solar-thermal system. It should be noted that initial low fluid conditions detected 305 and reported by the controller 170 are often very brief. However, the early notice provided allows service to be initiated prior the system suffering significant, possibly fatal, damage.

Potentially fatal pump damage may also occur if there is a loss of pressure within the potable water portion 191. Pressure loss may occur within the potable water portion 191 as a result of maintenance work on the potable water portion 191. In one embodiment, the controller 170 prevents this by monitoring the fluid level within the potable water portion 191 using the process depicted in the flowchart of FIG. 4. Specifically, the controller 170 receives information from the pressure transducer 180 a. If the controller 170 detects 405 a pressure drop in the potable water portion 191, the controller 170 shuts down 410 all operating pumps. In one embodiment, the controller 170 shuts down only the potable pump 160 a. Then, the controller 170 transmits 415 one or more alerts over the network 185 to report the loss of pressure within the potable water portion 191. An alert may be transmitted 415 via email, a short message service (SMS), or any other suitable method for transmitting 415 an alert over the network 185.

In one embodiment, the alerts notify service personnel or the owners of the system of the pressure loss, allowing appropriate service actions to be performed on the solar-thermal system.

Glycol Systems

FIG. 5 a illustrates one embodiment of a glycol system. As stated above, this system typically uses glycol which acts as an antifreeze agent to prevent freeze damage to solar thermal collectors. It will be apparent that other antifreeze agents can be used in conjunction with the present invention. There are many similarities between the glycol system illustrated in FIG. 5 a and the drain-back system illustrated in FIG. 1 a. For example, the glycol system is also comprised of two portions: a closed-loop portion 590 and a potable water portion 591. Again, a primary function of the closed-loop portion 590 is to heat a fluid using solar energy. A heat exchanger 135 transfers thermal energy from fluid circulating in the closed-loop portion 590 to potable water circulating in the potable water portion 591, thereby heating the potable water. Again, a primary function of the potable water portion 591 is to deliver heated potable water to a hot water output 102. Again, the heat exchanger 135 couples the two portions 590, 591. For illustrative clarity, however, the heat exchanger is presented herein as included solely within the closed-loop portion 591.

The closed-loop portion 590 includes a solar thermal collector 105. The solar thermal collector 105 absorbs solar energy and imparts thermal energy to fluid passing through it. In some embodiments, the closed-loop portion 190 includes multiple solar thermal collectors 105, thereby increasing the capacity of the system to collect solar energy and heat fluid. In such embodiments, the solar collectors 105 are typically interconnected such that they collectively operate upon a single fluid reservoir. The closed-loop portion 590 also includes a closed-loop pump 110 with an input port and an output port, an expansion tank 515, valves 125 a, 125 b, a first relief valve 130 a, and the heat exchanger 135. The closed-loop portion 590 also includes a third temperature sensor 140 c and a second pressure transducer 180 b.

The potable water portion 590 includes a storage tank 145, a water heater 150, a first potable pump 160 a with an input port and an output port, a second potable pump 160 b with an input port and an output port, a flowmeter 165, valves 125 c . . . 125 g, relief valves 130 b, 130 c, a mixing valve 155, a first temperature sensor 140 a, a second temperature sensor 140 b, and a first pressure transducer 180 a. The valves 125 a . . . 125 f, the relief valves 130 a . . . 130 c, and the flowmeter 165 each have an input and an output. The mixing valve 155 has two inputs and an output.

Referring now to FIG. 5 b, the closed-loop portion 590 of the glycol system of FIG. 5 a is detailed. As mentioned above, a primary function of the closed-loop portion 590 is to heat a fluid using solar energy. This is done by circulating the fluid through at least one solar thermal collector 105.

A closed-loop fill source 103 supplies fluid for the closed-loop portion 590. In one embodiment, the fluid is a mixture of glycol and water or pure glycol. In other embodiment, the fluid is oil. Hereinafter, any such mixture is referred to simply as glycol. The closed-loop fill source 103 connects to the input port of the second valve 125 b. As such, the second valve 125 b regulates the inflow of fluid into the closed-loop portion 590. The output port of the second valve 125 b connects to a first port of the heat exchanger 135. The second pressure transducer senses the pressure of the glycol within the closed-loop portion 591 and is positioned on a fluid line passing between the output port of the second valve 125 b and the first port of the heat exchanger 135. A second port of the heat exchanger 135 connects to the input port of the closed loop-pump 110. The output of the closed-loop pump 110 connects to both an input/output port of the expansion tank 515 and a first port of the solar thermal collector 105. The third temperature sensor 140 c senses the temperature of the glycol passing through the solar thermal collector 105. A second port of the solar thermal collector 105 connects to the first port of the heat exchanger 115.

In addition to the output port of the closed-loop pump 110, the input/output port of the expansion tank 115 also connects to both the input of the first valve 125 a and the input of the first relief valve 130 a. The output of the first relief valve 130 a connects to a first vent 104 a. The output of the first valve 125 a connects to a second vent 104 b.

Thus, a closed loop exists via which glycol may flow through the solar thermal collector 105, the heat exchanger 135, and the closed-loop pump 110. The closed-loop pump 110 pumps the glycol around the closed loop. The solar thermal collector 105 heats the glycol as it flows through the closed loop. The antifreeze properties of the glycol prevent freeze damage to the solar thermal collector 105. As the glycol circulates, the heat exchanger 135 transfers thermal energy from the glycol in the closed-loop to water in a potable water portion 591 of the solar thermal system which also flows through the heat exchanger 135 via a third and a fourth port. It is important to note that the glycol and the water from the potable water portion 591 do not mix within the heat exchanger 135. Only thermal energy is transferred between the two.

Referring now to FIG. 5 c, the potable water portion 591 of the glycol system of FIG. 5 a is detailed. As mentioned above, a primary function of the potable water portion 591 is to deliver heated potable water to a hot water output 102. This is done by circulating potable water through the heat exchanger 135 (shown as part of closed-loop portion 590 in FIG. 5 a and FIG. 5 b) and storing the subsequently heated water for later delivery.

A water supply 101 (e.g., a cold water supply) provides water for the potable water portion 591. The water supply 101 connects to the input port of the fifth valve 125 e. As such, the fifth valve 125 e regulates the inflow of water into the potable water portion 591. The output port of the fifth valve 125 e connects to both the first input of the mixing valve 155 and a first port of the flowmeter 165. The first temperature sensor 140 a senses the temperature of the water passing between the fifth valve 125 e and the flowmeter 165. A second port of the flowmeter 165 connects to a first port of the storage tank 145.

A second port of the storage tank 145 connects to the input port of the first potable pump 160 a. The output port of the first potable pump 160 a connects to the third port of the heat exchanger 135. The fourth port of the heat exchanger 135 connects to both the input of the third valve 125 c and the input of the fourth valve 125 d. The first pressure transducer 180 a senses the pressure of the water within the potable water portion 591.

The output of the third valve 125 c connects to a third vent 104 c. The output of the fourth valve connects to a third port of the storage tank 145. As such, the fourth valve 125 d regulates the flow of water between the heat exchanger 135 and the storage tank 145. A fourth port of the storage tank 145 connects to a first port of the water heater 150. The second temperature sensor 140 b senses the temperature of the water passing between the storage tank 145 and the water heater 150. A second port of the water heater 150 connects to the second input of the mixing valve 155. Thus, the mixing valve 155 combines water from the water supply 101 with water from the water heater 150 to produce water of a desired temperature. The output of the mixing valve 155 connects to the input of the sixth valve 125 f. The output of the sixth valve 125 f regulates a hot water supply 102 for the building being served by the glycol system.

The potable water portion 591 is also fed by a hot water return 507. The hot water return 507 connects to the input of the seventh valve 125 g, the output of which connects to the input of the second potable pump 160 b. The output of the second potable pump 160 b connects to the input of the eight valve 125 h, the output of which connects to the input of the flowmeter 165. Thus, water flows from the hot water return 507 to the first port of the storage tank 145.

To relieve pressure within the potable water portion 591, additional ports on the storage tank 145 and the water heater 150 connect to the inputs of the second relief valve 130 b and the third relief valve 130 c respectively. The outputs of the second relief valve 130 b and the third relief valve 130 c connect to a fourth vent 104 d.

Within, the potable water portion 591, water initially flows from the water supply 101 to the storage tank 145. The water is then pumped by the potable pump 160 a through the heat exchanger 135 where it gains heat transferred from the glycol in the closed-loop portion 590. The water then flows from the heat exchanger 135 into the storage tank 145. Thus, the heat exchanger 135 stores heated water for later use. Heated water also flows from the storage tank 145 into the water heater 150 which is able to provide supplementary heating of the water, if necessary, before it is flows to the hot water output 102.

Referring now to FIG. 5 d, a block diagram of one embodiment of a system for controlling the glycol system of FIG. 5 a is presented. The system comprises a controller 170 which is communicatively coupled to a network 185. In one embodiment of the present invention, the network 185 is a partially public or a wholly public network such as the Internet. The network 190 can also be a private network or include one or more distinct or logical private networks (e.g., virtual private networks or wide area networks). Additionally, the communicative coupling between the controller 170 and the network 185 can be wire line or wireless (i.e., terrestrial- or satellite-based transceivers).

The controller 170 is also communicatively coupled to the closed-loop pump 110, the first potable pump 160 a, the second potable pump 160 b, the first pressure transducer 180 a, the second pressure transducer 180 b, the first temperature sensor 140 a, the second temperature sensor 140 b, the third temperature sensor 140 c, and the flowmeter 165. The network 185 is also communicatively coupled to a weather server 175. Thus, the controller 170 is able to communicate with the weather server 175 via the network 185.

In one embodiment, the controller 170 monitors the temperature and pressure of water within the potable water portion 591 using information from the first temperature sensor 140 a, the second temperature sensor 140 b and the first pressure transducer 180 a. In one embodiment, the controller 170 also monitors the quantity of water within the potable water portion 591 using information from the flowmeter 165. The controller 170 monitors the glycol pressure within the closed-loop portion 590 using information from the second pressure transducer 180 b. In one embodiment, the controller 170 controls the operation of the closed-loop pump 110, the first potable pump 160 a, and the second potable pump 160 b.

As with drain-back systems, potentially fatal pump damage may also occur if there is a loss of pressure within either the closed-loop portion 590 or the potable water portion 591 of a glycol system. Pressure loss may occur as a result of overpressure and subsequent fluid release, leaky plumbing, or maintenance work on the solar thermal collector 105 or the potable water portion 191. In one embodiment, the controller 170 prevents such pump damage by monitoring the glycol level within the potable water portion 591 using the process depicted in the flowchart of FIG. 6. Particularly, the controller 170 monitors the status of both pressure transducers 180 b, 180 a. When the controller 170 detects 605 a pressure drop, the controller 170 determines 610 the location of the pressure drop. Specifically, the controller 170 determines if the pressure drop occurred 605 in the closed-loop portion 590 or the potable water portion 591 of the glycol system. In one embodiment, the controller 170 determines 610 the location by determining whether it was the first pressure transducer 180 a or the second pressure transducer 180 b that signaled the pressure drop. In one embodiment, this is done by coupling the first pressure transducer 180 a to a first input pin of the controller 170 and programming the controller 170 to treat all activity associated with the first input pin as corresponding the first pressure transducer 180 a and therefore the potable water portion 590. Similarly, the second pressure transducer is coupled to a second input pin of the controller and the controller 170 is programmed to treat all activity associated with the second input pin as corresponding to the second pressure transducer 180 b and therefore the closed-loop portion 590.

If the controller 170 determines 610 that the pressure drop was in the closed-loop portion 590, the controller 170 shuts down 615 all operating pumps. In one embodiment, the controller 170 shuts down only the closed-loop pump 110. Then, the controller 170 transmits 620 one or more alerts over the network 185 to report the loss of pressure within the closed-loop portion 590. An alert may be transmitted 620 via email, a short message service (SMS), or any other suitable method for transmitting 620 an alert over the network 185. In one embodiment, the alerts notify service personnel or the owners of the system of the pressure loss within the closed-loop portion 590, allowing appropriate service actions to be performed on the solar-thermal system.

If the controller 170 determines 610 that the pressure drop was in the potable water portion 591, the controller subsequently shuts down 625 only those pumps in the potable water portion 519 (e.g., the first potable pump 160 a and the second potable pump 160 b). This is because, depending on conditions, turning off the closed-loop pump 110 and the resulting stagnation of the glycol may risk overheating the glycol. When the temperature of glycol rises above a certain threshold, referred to herein as the acidic threshold, the glycol may transform from an inert fluid into an acid. The actual temperature of the acidic threshold depends on the exact composition of the glycol. Should the glycol become acidic, severe damage to the closed-loop portion 590 could result. Possible damage could include corrosion of pipes, the heat exchanger 135, the closed-loop pump 110, or other elements of the closed-loop portion 590. Thus, the controller 170 initially shuts down 625 only the potable pumps 160 a, 160 b.

After shutting down 625 the potable pumps 160 a, 160 b, the controller 170 transmits 630 one or more alerts over the network 185 to report the loss of pressure within the closed-loop portion 590. An alert may be transmitted 630 via email, a short message service (SMS), or any other suitable method for transmitting 630 an alert over the network 185. In one embodiment, the alerts notify service personnel or the owners of the system of the pressure loss within the potable water portion 591, allowing appropriate service actions to be performed on the solar-thermal system.

The controller 170 then determines 635 the risk of glycol overheating given current environmental conditions. At any time, many environmental factors can influence the risk that the temperature of the glycol will exceed the acidic threshold. Such factors include ambient temperature, level of direct sunlight, and wind conditions. In one embodiment, the controller 170 communicates with the weather server 175 to receive weather information pertinent to the period during which low pressure is experienced. In one embodiment, weather information may be obtained in advance (e.g., the controller 170 periodically receives weather forecasts from the weather server 175 and stores the received information along with a timestamp in the storage module 215). In an alternative embodiment, the controller 170 retrieves weather information from the weather server 175 only after detecting 605 a pressure drop. The solar thermal collector 105 is the element most responsible for heating the glycol. Thus, in one embodiment, the controller 170 receives information regarding the temperature of the solar thermal collector 105 directly from the third temperature sensor 140 c, which senses the temperature of the glycol passing through the solar thermal collector 105. It should be noted that, in various embodiments, the controller 170 may employ any combination of the above techniques to obtain information related to the risk of the glycol overheating.

After determining 635 the risk of glycol overheating by analyzing the environmental conditions as described above, the controller 170 calculates 640 an appropriate delay to minimize the risk of glycol overheating based on the risk and environmental conditions. The controller 170 the shuts down 645 the closed-loop pump 110 after the appropriate delay. In one embodiment, an appropriate delay is a delay sufficient for environmental conditions to change such that the risk of glycol overheating is reduced by some amount (e.g., a delay until the sun goes down, a delay until clouds move in, etc.). It should be noted that, under certain environmental conditions, an appropriate delay may be calculated 640 as very small, in which case the closed-loop pump 110 is shut down 645 almost immediately after the potable pumps 160 a, 160 b are shut down 625. Alternatively, certain environmental conditions may require that the closed-loop pump 110 never shuts down 645, in which case the delay may be calculated 640 as infinite. Any length of delay is possible.

In another embodiment, after calculating 640 an appropriate delay, the controller 170 continues to monitor the temperature of the glycol using information obtained directly from the third temperature sensor or indirectly from the weather server 175 as described above. If the glycol increases in temperature above a certain threshold, referred to herein as the pump damage threshold, the controller 170 shuts down the closed-loop pump 110, independent of the calculated delay 640. This protects the closed-loop pump 110 from damage due to overheating. The controller 170 then issues an alert over the network 185. The controller 170 continues to monitor the temperature of the glycol and issues an alert if it subsequently increases beyond the acidic threshold.

During a power outage, the closed-loop pump 110 is unable to circulate the glycol through the closed-loop portion 590. Thus, the glycol in the closed-loop portion 590 can also overheat, turn acidic, and damage the system as a result of a power outage. In one embodiment, the controller 170 prevents this by responding to a power outage using the process depicted in the flowchart of FIG. 7. When power is restored to the system, the controller 170 detects 705 that a restart has occurred. The controller 170 then determines 710 the duration that the system was without power. In one embodiment, the controller 170 periodically obtains date and time information via the network 185 and stores this information in a designated register within the storage module 215. After detecting a restart 705, the controller 170 determines 710 the duration of the power outage by comparing present date and time information with the contents of the designated register, which would represent the most recently stored date and time prior to the power outage.

The controller 170 analyzes 715 weather information related to environmental conditions during the outage. This analysis may be done using information obtained from the weather server 175 via the network 185, directly from the third temperature sensor 140 c, or both in accordance with the methods described above in reference to FIG. 6. The controller then determines 720 if the weather conditions during the outage were such that the glycol may have overheated, in which case an alert is issued. In one embodiment, event data related to power outages or other events in the past that may not have justified an alert or service response is stored in the storage module 215 of the controller 170. Though they did not warrant an alert, such past events may have affected the glycol's composition and its susceptibility to overheating. Thus, the controller 170 considers this stored event data along with the analyzed 715 weather information to determine 720 if an alert is needed. Accordingly, if the controller 170 determines 720 that an alert is not needed, it stores 725 information related to the event in the storage module 215 for later use. If the controller 170 determines 720 that an alert is needed, the controller 170 transmits 730 an alert over the network 185.

An alert may be transmitted 730 via email, a short message service (SMS), or any other suitable method for transmitting 730 an alert over the network 185. In one embodiment, the alerts notify service personnel or the owners of the system of the risk that the glycol may have become acidic, allowing appropriate service actions to be performed on the solar-thermal system.

Heat Exchanger Scaling

An additional concern for solar thermal systems, including both drain back and glycol systems, is scaling within the heat exchanger 135. Scaling refers to a buildup of mineral deposits due to mineral rich water which degrades the efficiency of the system. Accordingly, this is particularly a concern if a solar thermal system operates in an area with mineral rich potable water. In one embodiment, the controller 170 counteracts scaling in the heat exchanger 135 in accordance with the method depicted in the flowchart of FIG. 8.

The controller 170 periodically calculates 805 the solar thermal output of the system. Solar thermal output is calculated in two steps. First, the controller 170 calculates the difference in temperature between water flowing into the storage tank 145 (as measured by the first temperature sensor 140 a) and water flowing out of the storage tank 145 (as measured by the second temperature sensor 140 b). Second, the controller 170 multiplies this temperature difference by a flow rate (as measured by the flowmeter 165). In one embodiment, the controller 170 also maintains a timeline of operational hours (“pump hours”). Thus, a calculated 805 solar thermal output measurement is associated with a timestamp in the context of pump hours, allowing output to be analyzed 810 in a historical context.

Based on the presently calculated 805 output and the analyzed 810 historical output of the system, the controller 170 determines 815 if output has degraded sufficiently to warrant an alert. In one embodiment, this determination 815 is made by subtracting present output from the maximum output previously observed, thereby quantifying the degradation. The degradation may then be compared against a threshold. If degradation has exceeded the threshold (815), the controller 170 transmits 825 one or more alerts over the network 185 to report the condition, allowing de-scaling service activities to be scheduled. An alert may be transmitted 825 via email, a short message service (SMS), or any other suitable method for transmitting 825 an alert over the network 185. If degradation has not exceeded the threshold (815), the controller 170 stores 820 the output data with a timestamp for later use. In one embodiment, the output data is stored 820 in the storage module 215.

Additional Considerations

Some portions of above description describe the embodiments in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof. For example, the disclosed embodiments may be implemented as computer programs comprising instructions that can be stored on one or more computer readable storage mediums and such instructions are executable by a processor.

As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

Some embodiments may be described using the expression “coupled” and “connected” along with their derivatives. It should be understood that these terms are not intended as synonyms for each other. For example, some embodiments may be described using the term “connected” to indicate that two or more elements are in direct physical or electrical contact with each other. In another example, some embodiments may be described using the term “coupled” to indicate that two or more elements are in direct physical or electrical contact. The term “coupled,” however, may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. The embodiments are not limited in this context.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for a system and a process for controlling drain-back or glycol solar thermal systems through the disclosed principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims. 

1. A system for controlling the operation of a solar thermal system in a drain-back configuration, the system comprising: a fluid level switch positioned to sense a fluid level within a closed loop of the system; a pressure transducer positioned to sense a pressure drop within the system; and a controller coupled to the fluid level switch and the pressure transducer and a network.
 2. The system of claim 1, wherein the controller is configured to: turn off a pump within the closed loop and transmit an alert over the network in response to the fluid level switch indicating the fluid level being below a threshold.
 3. The system of claim 1, wherein the controller is configured to: responsive to the pressure transducer indicating a pressure drop, turn off a pump within the system and transmit an alert over the network.
 4. A system for controlling the operation of a solar thermal system in a drain-back configuration, the system comprising: a drain-back tank; a fluid level switch positioned within the drain-back tank to sense a fluid level within a closed loop of the system; a controller coupled to the fluid level switch and a network, the controller configured to turn off a pump within the closed loop and transmit an alert over the network in response to the fluid level switch indicating the fluid level being below a threshold.
 5. A system for controlling the operation of a solar thermal system in a drain-back configuration, the system comprising: a pressure transducer positioned to sense a pressure drop within the system; a controller coupled to the pressure transducer and a network, the controller configured to, responsive to the pressure transducer indicating a pressure drop, turn off a pump within the system and transmit an alert over the network.
 6. A system for controlling the operation of a solar thermal system in a glycol configuration, the system comprising: a first pressure transducer positioned to sense a pressure drop within a potable water portion of the system; a second pressure transducer positioned to sense a pressure drop within a closed loop of the system; a first temperature sensor positioned to sense a first temperature at a first location; a second temperature sensor positioned to sense a second temperature at a second location; a flowmeter positioned to sense a flow rate; and a controller coupled to the first pressure transducer and the second pressure transducer and the first temperature sensor and the second temperature sensor and the flowmeter and a network.
 7. The system of claim 6, wherein the controller is configured to: responsive to the first pressure transducer indicating a pressure drop: turn off a first pump in the potable water portion; transmit an alert over the network; determine a risk of a glycol fluid within the closed loop overheating; calculate a delay based on the risk; and turn off a second pump in the closed loop after the delay.
 8. The system of claim 6, wherein the controller is configured to: detect a restart of the system; determine a duration that the system was without power; determine a risk of a glycol fluid overheating during the duration; and responsive to determining the risk as above a threshold, transmit an alert over the network.
 9. The system of claim 6, further comprising a heat exchanger, wherein the controller is configured to report scaling in the heat exchanger.
 10. A system for controlling the operation of a solar thermal system in a glycol configuration, the system comprising: a first pressure transducer positioned to sense a pressure drop within a potable water portion of the system, the first pressure transducer coupled to a controller; a second pressure transducer positioned to sense a pressure drop within a closed loop of the system, the second pressure transducer coupled to the controller; the controller coupled to a network and configured to, responsive to the first pressure transducer indicating a pressure drop: turn off a first pump in the potable water portion; transmit an alert over the network; determine a risk of a glycol fluid within the closed loop overheating; calculate a delay based on the risk; and turn off a second pump in the closed loop after the delay.
 11. The system of claim 10, wherein determining the risk of the glycol fluid overheating comprises: analyzing data related to one or more environmental conditions of the solar thermal system; and determining a likelihood that a temperature of the glycol fluid will exceed a threshold.
 12. The system of claim 10, the controller further configured to, responsive to the second pressure transducer indicating a pressure drop: turn off all pumps within the system; and transmit an alert over the network.
 13. A system for controlling the operation of a solar thermal system in a glycol configuration, the system comprising a controller coupled to a network, the controller configured to: detect a restart of the system; determine a duration that the system was without power; determine a risk of a glycol fluid overheating during the duration; and responsive to determining the risk as above a threshold, transmit an alert over the network.
 14. The system of claim 13, wherein determining the risk of the glycol fluid overheating during the duration comprises: analyzing data related to one or more environmental conditions of the system during the duration.
 15. The system of claim 14, wherein determining the risk of the glycol fluid overheating during the duration further comprises: analyzing data related to one or more prior system events; and responsive to determining the risk as below a threshold, storing data related to the duration as a system event.
 16. A system for reporting scaling in a heat exchanger of a solar thermal system, the system comprising a controller coupled to a network and configured to: calculate a present solar thermal output for the system; compare the present solar thermal output to a previously calculated solar thermal output; and responsive to the difference between the present solar thermal output and the previously calculated solar thermal output exceeding a threshold, transmit an alert over the network.
 17. The system of claim 16, further comprising: a first temperature sensor positioned to sense a first temperature at a first location, the first temperature sensor coupled to a controller; a second temperature sensor positioned to sense a second temperature at a second location, the second temperature sensor coupled to the controller; a flowmeter positioned to sense a flow rate; and wherein calculating a solar thermal output for the system comprises calculating a difference between the first temperature and the second temperature and multiplying the difference by a flow rate.
 18. A method for controlling the operation of a solar thermal system in a drain-back configuration, the method comprising: responsive to detecting that a fluid level within a closed loop of the system is below a threshold, turning off a pump within the closed loop; and transmitting an alert.
 19. A method for controlling the operation of a solar thermal system in a drain-back configuration, the method comprising: responsive to detecting a pressure drop within the system, turning off a pump within the system; and transmitting an alert.
 20. A method for controlling the operation of a solar thermal system in a glycol configuration, the method comprising: responsive to detecting a pressure drop within the system, determining a location of the pressure drop; responsive to determining the location as within a potable water portion of the system: turning off a first pump in the potable water portion; transmitting an alert; determining a risk of a glycol fluid within a closed loop overheating; calculating a delay based on the risk; and turning off a second pump in the closed loop after the delay.
 21. The method of claim 20, wherein determining the risk of the glycol fluid overheating comprises: analyzing data related to one or more environmental conditions of the solar thermal system; and determining a likelihood that a temperature of the glycol fluid will exceed a threshold.
 22. The method of claim 20, further comprising, responsive to determining the location as within the closed loop: turning off all pumps within the system; and transmitting an alert over the network.
 23. A method for controlling the operation of a solar thermal system in a glycol configuration, the method comprising: responsive to detecting a restart of the system: determining a duration that the system was without power; determining a risk of a glycol fluid overheating during the duration; and responsive to determining the risk as above a threshold, transmitting an alert.
 24. The method of claim 23, wherein determining the risk of the glycol fluid overheating during the duration comprises: analyzing data related to one or more environmental conditions of the system during the duration.
 25. The method of claim 24, wherein determining the risk of the glycol fluid overheating during the duration further comprises: analyzing data related to one or more prior system events; and responsive to determining the risk as below a threshold, storing data related to the duration as a system event.
 26. A method for reporting scaling in a heat exchanger of a solar thermal system, the method comprising: calculating a present solar thermal output for the system; comparing the present solar thermal output to a previously calculated solar thermal output; and responsive to the difference between the present solar thermal output and the previously calculated solar thermal output exceeding a threshold, transmitting an alert.
 27. The method of claim 26, wherein calculating a solar thermal output for the system comprises: calculating a difference between a first temperature at a first location and a second temperature at a second location; and multiplying the difference by a flow rate. 